The present invention relates to a silver halide photographic light sensitive material spectrally sensitized in infrared region and a light sensitive, lithographic printing plate material utilizing silver complex diffusion transfer process.
With recent rapid progress of information transmitting systems, silver halide photographic light sensitive materials have been increasingly required to have high sensitivity. Such systems are, for example, high speed phototypesetting system according to which information output from electronic computer is immediately displayed as letters or figures by cathode ray tube and press facsimile system for rapid transmission of news paper originals to a remote place.
Characteristics required for silver halide photographic light sensitive materials for these uses are high sensitivity to so-called high intensity-short time exposure (flash exposure), namely, exposure for 10.sup.-4 second or less with light sources, e.g., lasers such as cathode ray tube (CRT), helium-neon gas laser and light emission diode (LED), high contrast and high resolving power.
The method of using laser light sources such as helium-neon and argon as a scanning type light source has the defects that large and expensive devices are necessary and efficiency of consumed power is low. On the other hand, semiconductor laser has the advantages that it is small in size, inexpensive, easily modulatable and long in life. For semiconductor laser, there are used semiconductors of such systems as Ga/As/P; Ga/Al/As; Ga/As; In/P; In/As and the like and wavelength of these laser beams is generally longer than 700 nm and largely is longer than 750 nm.
Therefore, bright safelight can be used and thus handleability is good. However, light sensitive materials for infrared rays are generally not so high in sensitivity and inferior in shelf stability and various proposals have been made in an attempt to solve these problems. For example, a technique called supersensitization effect has been proposed according to which spectral sensitivity is markedly enhanced by adding a specifically selected organic compound in addition to spectral sensitizing dye. Reference may be made to, for example, triazine derivatives disclosed in U.S. Pat. Nos. 2,785,058 and 3,695,888, mercapto compounds having electronegative group disclosed in U.S. Pat. No. 3,457,078, benzotriazole derivatives disclosed in Japanese Patent Kokai No. 51-81613, quaternary salts disclosed in Japanese Patent Kokai No. 59-191032 and others disclosed in Japanese Patent Kokai Nos. 61-69063 and 61-27884. However, many of these supersensitization techniques provide unsatisfactory results such as insufficient sensitization, increase of fog and decrease in shelf stability.
As a result of the inventors' intensive research on silver halide photographic light sensitive materials for semiconductor laser beam which are free from the above mentioned problems, it has been found that some compounds are markedly effective for this purpose.
A lithographic printing plate which utilizes as ink receptive areas a transferred silver images produced by the silver complex diffusion transfer process has already been disclosed in Japanese Patent Kokoku No. 48-30562 and Japanese Patent Kokai Nos. 53-21602, 54-103104 and 56-9750.
In a typical embodiment of the silver complex diffusion transfer process suitable for making lithographic printing plates, a silver image is formed in the following way: When a light sensitive material comprising a support and, provided successively thereon, a subbing layer which serves also as antihalation layer, a silver halide emulsion layer and a physical development nuclei layer is imagewise exposed and developed, the silver halide in the latent image area changes into developed silver in the emulsion layer. At the same time, the silver halide in non-latent image area dissolves by the action of a silver halide complexing agent contained in the developer and diffuses to the surface. The dissolved and diffused silver complex is precipitated by the reducing action of the developing agent on the physical development nuclei in the surface layer to form a silver image. After the development, if necessary, the silver image is subjected to sensitization treatment to enhance its ink recepticity. The material thus treated is mounted on an offset printing machine and the inked image is transferred to a print material.
In the conventional process, the silver halide emulsion layer is spectrally sensitized with a merocyanine dye, cyanine dye and the like so as to show a sensitivity maximum at around 550 nm green region. The emulsion layer is exposed in a process camera to a ordinary light source such as a tungsten bulb for several seconds to several tens of seconds. A printing plate obtained in this way, however, exhibited only limited sharpness and resolving power, even though an aforementioned sensitive material inherently excellent in these properties has been used. Moreover, in reproducing a color print from a color original, the conventional process has disadvantages in that both procedures of preparing the sensitive material and making a printing plate are troublesome in addition to the insufficient resolving power.
At present, plate making with laser beam has been proposed as one method for solving the above problems. For example, U.S. Pat. No. 4,501,818 and Japanese Patent Kokai Nos. 59-71055, 60-75838 and 60-100148 disclose lithographic printing plates which are exposed to light sources such as neon-helium laser and light-emitting diodes. As mentioned in these patent and patent publications, in these lithographic printing plates which utilize silver complex diffusion transfer process, the surface physical development nuclei layer affects the spectral sensitization and as a result, there occurs reduction of sensitivity to a laser beam or deterioration in the shelf stability. Further, since the silver complex diffusion transfer process produces a transferred and precipitated silver image of soft gradation, there occur a decrease in both sharpness and resolution of image, staining and worn-off of silver image during printing. These defects result in insufficient printing endurance and detract much from the printing plate quality. Therefore, a desirable sensitizing dye should meet all of the following requirements: sufficiently high sensitivity to the radiation wavelengths from lasers; good shelf stability; formation of transferred and precipitated silver image of high contrast; no adverse effects such as staining; and formation of a transferred and precipitated silver image having a sufficient adherence to keep even small silver grains from worn-off during printing.
There are known various lasers, but the methods of using laser light sources such as helium-neon and argon as a scanning type light sources has the defects and, on the other hand, semiconductor lasers have the advantages as explained hereinabove.
Light sensitive lithographic printing plate materials which utilize such semiconductor laser beams of long wavelength as a light source for imagewise exposure are disclosed in Japanese Patent Application Nos. 60-244880, 60-245059, 60-254202, 60-280426 and 60-284046.
However, it is known that silver halide photographic materials containing a sensitizing dye having a spectral sensitivity maximum in the wavelength region longer than 700 nm are generally inferior in shelf stability. This defect is conspicuous in lithographic printing plate having a physical development nuclei layer contiguous to an emulsion layer and sometimes it is already low in sensitivity or in printing endurance just after production thereof. One reason therefor is that the sensitizing dye undergoes desorption or decomposition with other substances in the silver halide emulsion layer.
According to the inventors' study, it has been found that these defects are improved by increasing the proportion of binder (mainly gelatin) to silver halide in silver halide emulsion layer, but increase the amount of binder inhibits precipitation of transferred silver, resulting in problems in printability. Thus, there is needed a method for solving the problems without giving adverse effect on printability. It is also necessary to gain further higher sensitivity to semiconductor laser beams.